Question: What is the Molten Salt Fast reactor and what will it do? Will it be a sustainable energy source or something completely different?

Emily Lewis answered on 5 Mar 2019:

A good question 🙂

Firstly, what is a molten salt reactor?
The main thing that makes it different from normal power plants is that instead of solid nuclear fuel rods made of uranium, we have decided to melt our uranium into some salt (a chloride or a fluoride) and then have it as a hot liquid in the reactor instead. This is where the Molten Salt in the name comes from.

This sounds a little bonkers I know. The reasoning behind it is that in an emergency it’s really easy to open a hatch at the bottom of the core and then drain out the fluid quickly into some separate drain tanks. This will stop the reactor from overheating and going supercritical (which means starting a runaway nuclear reaction, not good!). In a normal reactor you would have to yank out your fuel rods manually, but this way you get gravity to do all the work. So really the main reason is that the MSFR could be quite a bit safer!

The Fast bit in the name comes from the fact we are using the fast neutron spectrum, which means that our neutrons coming out of the reaction have a lot of energy each. This is good because we can extract a lot of energy at a high efficiency, but it does mean that we need to replace our parts more often.

Is it a sustainable energy source?
There is a lot of arguing over the answer this question. To tackle it let’s talk about what the word sustainable means- Wikipedia says a sustainable energy source “meets the needs of the present without compromising the ability of future generations to meet their own needs”
In practice, this means that the source shouldn’t realistically run out and shouldn’t damage the environment through global warming or otherwise.

Nuclear power stations don’t produce carbon emissions during operation, so we don’t contribute to global warming in this way. (There is energy cost and carbon contributions when we build them, but this applies to all energy sources and can’t currently be avoided.)

However it will produce nuclear waste, which when improperly managed can damage the environment. This is a problem with all nuclear reactors. Our best solution so far is to treat and seal the waste then keep it in a containment building until it stops being radioactive. This can be done safely and we know how, we just need to be really careful. MSFRs produce less waste than other designs because- it can “eat” used fuel from other reactors!

This leads into whether MSFRs are a sustainable from a fuel perspective. Normal reactors use uranium-233, and there is only a limited amount of it in the earth’s crust, enough for about 200 years. There are ways of getting it out of seawater which are being researched, but really normal nuclear power is not considered sustainable because of this.

MSFRs on the other hand as I said earlier, can burn used up fuel from other reactors and from themselves. This means we can take the waste that our reactor makes and feed in back in as fuel. We call this a ‘breeder’ reactor as it is making more fuel than we burn and it would count as a sustainable fuel source.

So I hope I’ve given you enough information to help you make up your mind about the answer or inspired you to go and find out more!
At the end of the day, it’s quite a weird little design but it comes with some interesting advantages. There are some people planning on building them in the USA and Europe so I hope I can tell you more with some experimental data in the coming years.